This invention pertains to an improved capacitive structure of a type comprising a group of capacitive layers, each of which includes a dielectric substrate and a metallized area on one surface of the dielectric substrate and which are arranged such that the metallized areas on alternate layers extend to opposite edges of the capacitive structure, and opposed masses of conductive material, each of which covers one such edge of the capacitive structure and provides electrical connections to the metallized areas extending to the same edge. A capacitive property is exhibited where the metallized areas overlie one another.
Capacitive structures of the type noted above are exemplified in U.S. Pat. Nos. 4,462,062, 4,488,340, and 4,531,268. These patents disclose that such a capacitive structure may be advantageously made by winding, in overlying relation on a drum, two webs of polymeric film, each providing a dielectric substrate. Each web of such film has a metallized coating on its upper surface, except for narrow, longitudinal, demetallized zones, which may be scribed by laser means, and which divide the metallized coating into a relatively wide metallized area extending to and along one edge and a relatively narrow metallized strip extending to and along the other edge. The webs, which are of equal width, are offset laterally such that as the webs are slit into parallel ribbons of uniform width before being wound on the drum, alternate ones of the successive layers of the overlying ribbons have their edges offset laterally in relation to the remaining layers. A conductive, metallic mass, which may be applied by a metal-spraying process, covers each edge of the overlying ribbons so as to provide electrical contacts to and between the metallized areas extending to and along such edge. The resultant structure, which is called a rope because it has a tendency to be somewhat limp, is compressed at an elevated temperature so as to form a more rigid structure, which is called a stick. The stick is sawed into discrete capacitors. In each capacitor, the conductive, metallic masses serve as electrodes, and a capacitive property is exhibited where the relatively wide metallized areas of the successive layers overlie one another.
It is known for an upper cover and a lower cover, each being a single, thicker plate of dielectric material, to cover the top and bottom surfaces of the group of capacitive layers and for each of the conductive, metallic masses to extend above the upper cover and below the lower cover so as to form respective upper and lower flanges, which bond the covers to the group of capacitive layers. The upper and lower covers provide mechanical and electrical protection to the capacitive structure. Moreover, if the capacitive structure is surface-mounted to a supporting substrate, the lower flanges elevate the lower cover in relation to the supporting substrate. Hence, the lower flanges may also be called stand-off feet or mounting feet. Typically, the capacitive layers and cover plates are built-up to a standardized thickness, e.g., 0.08 inch.
For further background, reference may be had to U.S. Pat. Nos. 3,670,378 and 4,229,865, which disclose other examples of capacitive structures of the type noted above.
Although capacitive structures of the type noted above as known heretofore have performed well in many applications, there has been a need, to which this invention is addressed, for improvements in such structures.